Remove outdated KEYS file from repository

[mawiesne]

Change

• removes outdated KEYS file from repository, as per ASF requirements the KEYS file should be published in a project's distribution directory
• see: https://infra.apache.org/release-distribution.html#sigs-and-sums

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[jzonthemtn]

Is the KEYS file moved somewhere else?

[rzo1]

@jzonthemtn the location for the KEYS file is the distribution area of OpenNLP which is here https://dist.apache.org/repos/dist/release/opennlp/KEYS